Lumia 720 with 8.1 hanged.

[Sai Teja4]

my lumia 720 got hanged , because of volume down button is not working i was unable to reset the phone.
then i installed NSU 4.1 firstly my phone responded to it and showed me some update but because it showed me a warning sign" data might be lost" i have canceled the update.
It ended up showing a NOKIA logo on the screen and now its not responding to NSU 4.1 now too.

Please help me out.